Apparatus for dispensing coffee or other beverage in response to the deposit of a coin or the actuation of a switch are well known in the art. In one type of such apparatus, a storage pan or reservoir is used to hold the previously prepared beverage prior to dispensing and to dispense the beverage from the storage pan through a controllable valve.
Various expedients have been employed in the prior art to control the amount of beverage delivered to a user. In some vending machines, the dispense valve is opened by actuation of a push-button switch that becomes operable if a coin is deposited. The valve does not close until the button is released. If a customer is able to position a second cup with one hand after the first cup is filled while keeping the button depressed with the other hand, he can obtain two or more cups for the price of only one. In other systems, the dispense valve is energized for a fixed time interval to dispense the desired amount of beverage. This method is highly unsatisfactory, however, since the flow rate is dependent on the pressure head from the reservoir, which varies directly with the level of beverage in the reservoir.
Still other systems employ a positive displacement technique in which a first valve is actuated to fill a chamber with beverage from the reservoir and a second valve then actuated to fill the cup from the chamber. While these systems insure the dispensing of a controlled amount of beverage irrespective of the level in the reservoir, they do not permit ready adjustment to dispense different amounts of beverage.